1. Field of the Invention
The present invention relates to an image forming apparatus and image forming method using the electrophotographic method and more specifically, to an image forming apparatus and image forming method with an improvement in a cleaning step for cleaning the spherical toner remaining on an image bearing member after a transfer step.
2. Related Background Art
In these days, a complex machine serving jointly for all output terminals such as copier, printer and facsimile has been widely accepted in the market. As such a network-ready terminal, the electrophotographic system is widely used. One of the problems to be solved in this electrophotographic system is to enhance the Duty Cycle of a main body. xe2x80x9cDuty Cyclexe2x80x9d means the limit of the number of sheets within which the main body continues operating normally without maintenance by a service person. One of the most crucial rate-determining factors in Duty Cycle is the service life of an image bearing member (hereinafter, also referred to as xe2x80x9cphotosensitive memberxe2x80x9d).
On the other hand, from the viewpoint of ecology, it is required to eliminate the waste, that is, to reduce the expendable, to prolong the service life of expendables and to promote the reliability of the expandables. Transit from a conventional analog machine to a new digital machine has advanced and the cost of a main body is also required to be made equal to or lower than that of an analog machine. Furthermore, in the field of a copier and a printer, a monochrome machine formerly constituted the main-stream, but recently, making a draft or an output file into full color is rapidly increasing in offices. In addition to making the cost of the main body in a digital machine equal to or lower than that of the analog machine as mentioned above, the main body cost and the running cost of a full-color copier or printer has been required to be equal to that of the monochrome machine. For this reason, a technique has been desired which enables TCO (Total Cost of Ownership: total necessary cost viewed from a user) to be dramatically reduced.
Under such circumstances, in recent years, a full-color image forming apparatus for transferring the respective color toner images, different in color, formed on individual photosensitive members to the transfer material carried on a transfer belt in successive overlap to obtain a color image, comprising multiple image bearing members and a transfer belt for carrying and conveying an image transferring material, quadruple tandem type full-color image forming apparatus has become main. In an image forming apparatus repeating the step of transferring a transferable image formed on the surface of an image bearing member to a transfer material chiefly made of paper, it is indispensable to fully remove the residual toner remaining on the image bearing member without transferring to the transfer material after the transfer.
Consequently, numerous proposals have so far been made as cleaning means, but means as scraping off the residual toner by means of a cleaning blade comprising an elastic material such as urethane rubber is widely put to practical use, because of being simple and compact in configuration, inexpensive and further excellent in tone removal function. As rubber material of a cleaning blade, urethane rubber is used in general which is high in hardness, rich in elasticity and outstanding in wear resistance, mechanical strength, oil resistance and ozone proof property.
The image bearing member comprises a photosensitive layer and protecting layer provided on a conductive support, while the outermost layer of this image bearing member contains fluorine-atom-contained resin fine particles and the used one is mechanically polished so as to set the 10 point average surface roughness Rz (hereinafter, referred to as xe2x80x9caverage surface roughnessxe2x80x9d) defined by JIS standard B061 to a moderate range. So far, it has been considered that the slidability between the outermost layer of the image bearing member and the cleaning blade is lost, the surface of the outermost layer is roughened by wear and micro-grained toner out of the residual toner during the transfer becomes likely to slip off through the surface if a value of this Rz is too small, whereas if a value of Rz is too large, a gap appears between the outermost layer of the image bearing member and the cleaning blade and the residual toner is likely to slip off though this gap.
In a system that plenty of scraped dust of the outermost layer of the image bearing member is generated and aggregated, the blade edge is instabilized and especially when high roundness toner is used, slip-off of toner actually occurs, so that a further improvement is desired for such a system.
Thus, it is desired to effectively prevent the occurrence of toner slip-off in the use of high roundness toner and to suppress the wear of the outermost layer of the image bearing member for the attainment of a long service life of a photosensitive member.
It is one object of the present invention to provide an image forming apparatus and an image forming method in which the above problems have been solved.
It is another object of the present invention to provide an image forming apparatus and an image forming method capable of accomplishing a good cleaning also for high roundness spherical toner.
It is another object of the present invention to provide an image forming apparatus and an image forming method capable of accomplishing a good cleaning also for high roundness spherical toner even if the wear of a photosensitive member is suppressed and the service life is prolonged.
It is another object of the present invention to provide an image forming apparatus comprising:
an image bearing member for bearing an electrostatic latent image;
a charging device for applying a voltage to the surface of the image bearing member to charge the surface thereof;
electrostatic latent image forming means for forming an electrostatic latent image on the surface of the image bearing member charged by the charging device;
developing means for adhering the toner carried on a toner carrying member to the electrostatic latent image formed on the surface of the image bearing member to form a toner image;
a transfer material carrying member for carrying and conveying a transfer material to the surface of the image bearing member;
transfer means for electrostatically transferring the toner image formed on the surface of the image bearing member to a transfer material; and
cleaning means for cleaning the image bearing member,
wherein the toner comprises toner particles with a shape factor SF-1 of 100 to 140 and a shape factor SF-2 of 100 to 120, the cleaning means comprises a cleaning blade brought into butt contact with the surface of the image bearing member in a counter direction at a line pressure N higher than 20 g/cm and lower than 60 g/cm, and the cohesive degree xcex1 of powder ranges from 10% to 60%, the powder including the scraped dust which is generated by wearing of the outermost layer surface of the image bearing member due to butt contact with the cleaning blade and accumulated at the edge of the cleaning blade.
It is another object of the present invention to provide an image forming method comprising:
a charging step of applying a voltage to the surface of the image bearing member to charge the surface thereof;
electrostatic latent image forming step of forming an electrostatic latent image on the surface of the charged image bearing member surface;
a developing step of adhering the toner carried on a toner carrying member to the electrostatic latent image formed on the surface of the image bearing member to form a toner image;
a transferring step of electrostatically transferring the toner image formed on the surface of the image bearing member to a transfer material; and
a cleaning step of cleaning the surface of the image bearing member after the transferring step by means of cleaning means;
wherein the toner comprises toner particles with a shape factor SF-1 of 100 to 140 and a shape factor SF-2 of 100 to 120, the cleaning means comprises a cleaning blade brought into butt contact with the surface of the image bearing member in a counter direction at a line pressure N higher than 20 g/cm and lower than 60 b/cm, and the cohesive degree xcex1 of powder ranges from 10% to 60%, the powder including the scraped dust which is generated by wearing of the outermost layer surface of the image bearing member due to butt contact with the cleaning blade and accumulated at the edge of the cleaning blade.